On Feb 7, 2009, at 11:59 PM, Antony Blakey wrote:
On 08/02/2009, at 3:07 PM, Damien Katz wrote:
I can't see why this needs to be the case. The fact that there are
peers that have an incomplete replication doesn't stop the master
taking updates - iff the updates to the master are multi-document
ACID.
Because during downstream replication it may get just some of the
documents from a commit that happens during replication.
Replication isn't all or nothing, and it doesn't know about
transactions
OK, I would have thought that a) replication was relative to a
specific MVCC commit; and b) a given user-level transaction was all
within a specific MVCC commit. So the replicator sees at least an
MVCC consistent view of the updates. Actually, I can't see how
replication that doesn't respect MVCC commits can work at all,
because the resultant data would be inconsistent with even the
weaker ACID that you've proposed.
No, CouchDB replication doesn't support replicating the transactions.
Never has, never will. That's more like transaction log replication
that's in traditonal dbs, a different beast.
For the new bulk transaction model, I'm only proposing supporting
eventual consistency. All changes are safe to disk, but the db may not
be in a consistent state right away.
The thing is, to avoid all conflicts and inconsistent states, you
must read lock the source db during active replication and write
lock the target database pretty much until the replication is
complete. Otherwise, you'll will get inconsistent states.
Locking for writes is obvious, but read locking the source isn't.
As it works now, if the source is updated while replicating, the
target may get some of the documents from those updates. Transactions
don't replicate.
Does each user get their own local instance of the database?
Not necessarily, and even if they did, it's likely that they'll have
multiple browser windows open.
What's the front end written in?
-Damien
Antony Blakey
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